I am not sure if this is cosplay, or one of those If They Mated moments.
It has the cosplay tag, but is in the touhou kids pool. so... that isn't any help either.

Basically, Satori can be anyone, she can read their danmaku pattern, cosplay it, and shove it at you.

If the source says its a child of Sanae X Satori, then its a child instead of a cosplay.